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    Atomically resolved imaging of highly ordered alternating fluorinated graphene
    (Nature Publishing Group, 2014) Kashtiban, Reza J.; Dyson, M. Adam; Nair, Rahul R.; Zan, Recep; Wong, Swee L.; Ramasse, Quentin; Geim, Andre K.
    One of the most desirable goals of graphene research is to produce ordered two-dimensional (2D) chemical derivatives of suitable quality for monolayer device fabrication. Here we reveal, by focal series exit wave reconstruction (EWR), that C2F chair is a stable graphene derivative and demonstrates pristine long-range order limited only by the size of a functionalized domain. Focal series of images of graphene and C2F chair formed by reaction with XeF2 were obtained at 80 kV in an aberration-corrected transmission electron microscope. EWR images reveal that single carbon atoms and carbon-fluorine pairs in C2F chair alternate strictly over domain sizes of at least 150 nm(2) with electron diffraction indicating ordered domains >= 0.16 mu m(2). Our results also indicate that, within an ordered domain, functionalization occurs on one side only as theory predicts. In addition, we show that electron diffraction provides a quick and easy method for distinguishing between graphene, C2F chair and fully fluorinated stoichiometric CF 2D phases.
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    Silicon-Carbon Bond Inversions Driven by 60-keV Electrons in Graphene
    (AMER PHYSICAL SOC, 2014) Susi, Toma; Kotakoski, Jani; Kepaptsoglou, Demie; Mangler, Clemens; Lovejoy, Tracy C.; Krivanek, Ondrej L.; Ramasse, Quentin
    We demonstrate that 60-keV electron irradiation drives the diffusion of threefold-coordinated Si dopants in graphene by one lattice site at a time. First principles simulations reveal that each step is caused by an electron impact on a C atom next to the dopant. Although the atomic motion happens below our experimental time resolution, stochastic analysis of 38 such lattice jumps reveals a probability for their occurrence in a good agreement with the simulations. Conversions from three- to fourfold coordinated dopant structures and the subsequent reverse process are significantly less likely than the direct bond inversion. Our results thus provide a model of nondestructive and atomically precise structural modification and detection for two-dimensional materials.